August 20, 1886.] 



SCIEjSTCE. 



175 



large one. But the comets, on the contrary, ap- 

 pear to have become aggregated in small masses. 

 The idea that heat was essential to the production 

 of these minerals was at first a natural one. All 

 other known rock formations are the result of pro- 

 cesses that involve water or fire or metamorphism. 

 All agree that the meteorites could not have been 

 formed in the presence of water or free oxygen. 

 What conclusion was more reasonable than that 

 heat was present in the form of volcanic or of meta- 

 morphic action? 



The more recent investigations of the meteorites 

 and kindred stones, especially the discussions of 

 the Greenland native irons and the rocks in which 

 they were imbedded, are leading mineralogists, if 

 I am not mistaken, to modify their views. Great 

 heat at the first consolidation of the meteoric mat- 

 ter is not considered so essential. In a late paper, 

 M. Daubree says : " It is extremely remarkable 

 that, in spite of their great tendency to a perfectly 

 distinct crystallization, the silicate combinations 

 which make up the meteorites are there only in 

 the condition of very small crystals, aU jumbled 

 together as if they had not passed through fusion. 

 If we may look about us for something analogous, 

 we should say that instead of calling to mind the 

 long needles of ice which liquid water forms as it 

 freezes, the fine-grained texture of meteorites re- 

 sembles rather that of hoar-frost, and that of snow, 

 which is due, as is known, to the immediate pas- 

 sage of the atmospheric vapor of water into the 

 solid state." So Dr. Reusch, from the examination 

 of the Scandinavian meteorites, concludes that 

 ' ' there is no need to assume volcanic and other 

 processes taking place upon a large heavenly body 

 formerly existing but which has since gone to 

 pieces." 



The meteorites resemble the lavas and slags on 

 the earth. These are formed in the absence of 

 water, and with a limited supply of oxygen, and 

 heat is present in the process. But is heat neces- 

 sary? Sorae crystallizations do take place in the 

 cold ; some are direct changes from gaseous to 

 soKd forms. We cannot in the laboratory repro- 

 duce all the conditions of crystaUization in the 

 cold of space. We cannot easUy determine whether 

 the mere absence of oxygen will not account fully 

 for the slag-like character of the meteorite miner- 

 als. Wherever crystallization can take place at aU, 

 if there is present silicon and magnesium and iron 

 and nickel, with a limited supply of oxygen, there 

 silicates ought to be expected in abundance, and the 

 iron and nickel in their metallic form. Except for 

 the heat, the process should be analogous to that 

 of the reduction of iron in the Bessemer cupola, 

 where the limited supply of oxygen combines with 

 the carbon and leaves the iron free. The smallness 



of the comets should not, then, be an objection to 

 considering the meteoric stones and irons as pieces 

 of comets. There is no necessity of assuming that 

 they were parts of a large mass, in order to pro- 

 vide an intensely heated birth-place. 



But although great heat was not needed at the 

 tu-st formation, there are many facts about these 

 stones which imply that violent forces have in 

 some way acted during the meteorites' history. 

 The brecciated appearance of many specimens, the 

 fact that the fragments in a breccia are themselves 

 a finer breccia, the fractures, infiltrations, and ap- 

 parent faultings seen in microscopic sections and 

 by the naked eye — these all imply the action of 

 force. M. Daubree supposes that the union of 

 oxygen and silicon furnishes sufficient heat for 

 making these minerals. If this is possible, those 

 transformations may have taken place in their 

 first home. Dr. Reusch argues that the repeated 

 heating and cooling of the comet, as it comes down 

 to the sun and goes back again into the cold, is 

 enough to account for all the peculiarities of struc- 

 ture of the meteorites. These two modes of action 

 do not, however, exclude each other. Suppose, 

 then, a mass containing silicon, magnesium, iron, 

 nickel, a limited supply of oxygen, and small 

 quantities of other elements, all in their primordial 

 or nebulous state (whatever that may be), segre- 

 gated somewhere in the cold of space. As the 

 materials consolidate or crystallize, the oxygen is 

 appropriated by the silicon and magnesium, and 

 the u'on and nickel are deposited in metalhc form. 

 Possibly the heat developed may, before it is radi- 

 ated into space, modify and transform the sub- 

 stance. The final result is a rocky mass (or pos- 

 sibly several adjacent masses), which sooner or 

 later is no doubt cooled down throughout to the 

 temperature of space. This mass, in its travels, 

 comes near to the sun. Powerful action is there 

 exerted upon it. It is heated. How intense is 

 that heat upon a cold rock, unprotected apjoar- 

 ently by its thin atmosphere, it is not possible 

 to say. We know that the sun's action is strong 

 enough to develop that immense train, the comet's 

 tail, that sometimes spans our heavens. It is 

 broken in. pieces. We have seen the portions go 

 off from the sun, to come back, probably, as sepa- 

 rate comets. Solid fragments are scattered from 

 it to tl•a^'el in their own independent orbits. What 

 is the condition of the burnt and crackled surface 

 of a cometic mass or fragment as it goes out from 

 the sun again into the cold ? What changes may 

 not that surface undergo before it comes back 

 again, to pass anew through the fiery ordeal ? We 

 have here forces that we know ai-e acting. They 

 are intense, and act under varied conditions. The 

 stones subject to those forces can have a history 



